One relatively recent development in termite control is the use of slow-acting toxicants for managing subterranean termite populations near structures. Many chemical “attractants” (pheromones and the like) have been proposed for use in such baits. See, e.g., WO 93/23998 and U.S. Pat. No. 5,571,967. However, there have been few if any demonstrations of true “attraction” of subterranean termites that forage in soil. The term “attractant” is often confused with or misused in place of “feeding stimulant,” or “arrestant” (which are chemical cues that cause the animals to aggregate near the chemical source). An “attractant” is “a chemical that causes animals to make orientated movement toward its sources” (Shorey, 1977). Semiochemicals are chemical substances that deliver behavioral messages to animals (Metcalf & Metcalf, 1975).
There are many patents that refer to the use of feeding stimulants in cellulose-based baits to increase termite feeding on baits. Some of the patents refer to “attractants,” but the data and proposed uses indicate that they actually involve “feeding stimulants” that increase termite feeding on baits rather than attractants that cause termites to “make orientated movement toward its sources.” For example, U.S. Pat. No. 6,093,389 relates to a steroid derivative in a cellulose-based termite bait. This reference states that the use of decayed or fungus-inoculated wood to attract termites is not satisfactory for commercial use. A food source is said to be an important component in the bait compositions of this patent.
U.S. Pat. No. 5,874,097 relates to the use of chemicals (naphthalene and others similar to nest extracts; identified in PAPERMATE ball-point pens that were found to elicit trail-following behavior in termites) to increase termite feeding on baits comprising cardboard, paper, sugar cane, corn cobs, and other cellulose mixtures. U.S. Pat. No. 5,637,298 uses 2-naphthalenemethanol in cellulose-based baits such as cardboard and paper to induce trail-following behavior and for feeding stimulation to increase the rate of bait consumption by termites. U.S. Pat. No. 3,858,346 uses “termite-attracting” carbohydrate (hexachlorocyclo-pentadiene dimer) in sawdust-based bait to increase termite feeding of baits.
Rust et al., Sociobiology, Vol. 28, No. 3, pp. 275-285 (1996), discuss attempts to use extracts of brown-rot fungus to increase the likelihood that wood stakes would be located by termites. Water was used in an attempt to disperse the extract in sand. It was noted that the extract was not soluble enough in water, and surfactants were used in an attempt to improve the effective depth that the fungal extract would penetrate the soil. Field studies of sweetgum blocks conditioned with the Gloecophyllum trabeum fungus “did not reveal any special attractiveness.” The conclusion of this reference was that additional research is needed to insure the longevity and maximal dispersion of such attractants in soil.
U.S. Pat. No. 6,203,811 uses a fungal extract as a “feeding stimulant” in cellulose-based baits to increase termite feeding on the baits.
Various patents relate to the feeding stimulants in wood blocks together with a slow-acting insecticide. Again, some of these patents might use the term “attractant,” but the data and proposed use indicate they do not and are not intended to “cause termites to make orientated movement toward its sources.” Thus, these are examples of “feeding enhancers.” U.S. Pat. No. 4,455,441 uses an “attractant termiticide” compound in a feeding block. U.S. Pat. No. 3,070,495 places wood blocks treated with fungi-decay extract and an insecticide in the ground; this might result in increased termite feeding but did not “attract” subterranean termites from any distance. U.S. Pat. No. 4,363,798 uses fungi-decayed wood blocks impregnated with borons (to kill termites).
In most or all of the art mentioned above, feeding stimulants or other “attractive” semiochemicals are incorporated in toxic baits, which are not intended for “monitoring.” U.S. Pat. No. 5,573,760 teaches a composition “preferred” by termites that is to be used for monitoring termites in soil before toxicant baits are installed. The data showed that the medium was “highly palatable” but did not demonstrate that it caused termites foraging in soil “to make orientated movement toward its sources.” Thus, that medium functioned as a feeding stimulant rather than as an “attractant.” The following portion from that patent clearly illustrates the difference between “attractants” and feeding stimulants:                It is important to note that the monitoring composition does not attract termites per se. One would not want to attract termites and create a problem where none existed before. However, because termites prefer consuming the monitoring composition, once the termites discover it, they will return to it and recruit others from the colony. Subterranean termites tunnel underground and will tunnel into the monitoring composition. The termites will stimulate other colony members to use the food, then return to the colony and share the food. These behavioral patterns are utilized to great advantage in the monitoring and controlling methods of the present invention.        
Consistent with this, the art heretofore taught that a cellulose-based food source was an essential element to make the baits sufficiently “attractive” to termites (even if pheromone “attractant” is also used). While the art mentions the use of pheromones to make baits more attractive, the art generally teaches that a cellulose/food source is needed in conjunction with the pheromone. U.S. Pat. No. 5,151,443 mentions that trail pheromones and decayed wood can be used with sawdust and the like in baits for controlling termites. U.S. Pat. No. 6,100,805 relates to a spike-shaped tube for termite detection. A conductive loop is present between two wooden blocks inside the tube. A pheromone can be formed over or blended within “electrically insulative protective material” that covers the conductive loop. The insulation can be a resin such as an epoxy resin, including two-part epoxy resins. However, the wooden blocks are treated as essential components. Apparently, a cellulose food source was deemed to be essential as an “attractant.” U.S. Pat. No. 5,571,967 relates to a termite-detecting electronic device. The device as illustrated has a can-like outer “casing” that is to be positioned primarily above ground. A wooden detecting sample (a cube of wood) is within the “casing.” As the detecting block is degraded, presumably by termites, such movement is detected by the electronic apparatus. The '967 patent states that a termite-guiding pheromone is used in order to “attract” termites to the detecting sample.
However, one major obstacle to the successful “real world” use of cellulose-based medium or baits that are placed in soil is their relatively short life. Thus, these references do not even identify a main problem with pheromones and cellulose-based baits: especially when used in hot and humid soil, the chemical attractants therein decompose too quickly to be of practical use for “attractant” delivery. It would be particularly advantageous to have monitoring devices that would last after eliminating the structure-infesting populations by the initial baiting, in which months or years may pass before new populations of subterranean termite migrate near the stations. Under these circumstances, an “attractant” would need to remain available in soil for months and sometimes years.
For commercial monitoring-baiting programs, the monitoring devices may have to remain in soil for 6-18 months before termites are detected in the stations. Most commercial baiting programs, such as the SENTRICON® Termite Colony Elimination System, involve a monitoring-baiting procedure that depends on the monitoring phase to detect termites before toxic baits are used.
There are other issues to be addressed in order to successfully use pheromones and baits. For example, U.S. Pat. No. 5,572,825 relates to a glue trap primarily for trapping cockroaches and the like. This patent acknowledges that aggregation pheromones might be used but notes that there are associated difficulties, such as identifying and characterizing a desired pheromone (which can be colony-specific) and maintaining the stability of such volatile hormones.
WO 93/23998 mentions the use of bait materials such as METHOCEL in a casing in a station housing. This application also states that pheromones (and the like) can be used to modify the monitoring device to increase the possibility that the target pest will enter and move within the device. However, it is also noted therein that trail pheromones can actually cause foraging termites to avoid eating the bait, and that reproducing functional synthetic pheromones can be very difficult (especially in light of the observation that different pheromones can be pest and colony specific).
U.S. Pat. No. 5,024,832 showed that the (3Z, 6Z, 8E)-dodecatrienol has a unique characteristic of inducing termite trail-marking. The embodiment described therein involved detecting and capturing foraging termites by placing a glass plate coated with this trail-marking pheromone on the surface of the soil. As with many behavior-modifying semiochemicals, however, (3Z, 6Z, 8E)-dodecatrienol is unstable in soil or in open air (as it reacts with oxygen). It thus degrades too quickly for practical use.
U.S. Pat. Nos. 6,079,151 and 6,058,646 discuss in more detail the species- and colony-specific nature of pheromones, as well as the difference between trail and feeding-initiating pheromones. The embodiments illustrated in these patents appear to be above-ground boxes for mounting to a structure. These patents state that pheromone mimics can make the matrix attractive or non-repellent to the pest species being monitored or controlled.
Some attempts have been made to attract termites without pheromones. U.S. Pat. No. 6,023,879 describes a device to deliver water in soil near bait stations to attract termites. U.S. Pat. No. 5,921,018 teaches an elaborate apparatus to collect and channel rainwater in soil near bait stations to capture and kill termites. U.S. Pat. No. 5,899,018 describes a device that uses the solar heating/night cooling cycle to deliver a moisture-absorbing “attractant” (cardboard, cow dung, wood, and the like) into soil to attract termites. On the other hand, U.S. Pat. No. 5,927,001 relates to a bait station having a tubular body (made of rigid foam or plastic like Styrofoam) with a triangular cross section; a triangular bait is fitted into the bait holder. The bait holder is designed to keep water away from the cardboard to prevent its degradation. The bait is impregnated with a toxicant. Pheromones are not mentioned in this patent.
U.S. Pat. No. 6,158,166 includes a discussion of materials that can be used as termite bait. Rigid foam such as Styrofoam is one suggestion. However, it is clearly noted therein that such materials are not actual food sources and thus are to be used in conjunction with natural wood products.
U.S. Pat. No. 4,043,073 relates to a container that encloses bait material for termites or other pests, wherein the bait has an odiferous material in it to signal to humans when the container has been attacked by pests. This patent mentions that a hormone can be added as an attractant to the container wall. These containers appear to be “permanently” buried in the ground without having the bait replaced. This patent does not teach or suggest the combination of advantages that using a pheromone in a SENTRICON-like housing would provide. While this patent, like many others, mentions hormones, this patent does not show any actual success of doing so.
U.S. Pat. No. 5,141,744 relates to a macrogel that can be in the form of a cone, funnel, tube, or spike wherein the macrogel contains an entomopathogen attractant such as fungal-decayed wood. U.S. Pat. No. 5,504,142, entitled “Device for Controlling Insects,” relates to a mixture comprising a thermoplastic elastomer and at least one chemical mediator (including pheromones) that acts on the behavior of insects and acarids. The invention is designed for treating crops against insects and acarids. The mixture can take the form of granules or sticks.
The '142 patent cites Japanese Application 81 JP-024042, published as KOKAI JP 57 139005, as describing compositions of pheromones and of a binder containing 4 to 20% of pheromones. The binder is silicone or SBR rubber. A solvent such as methylene chloride, benzene, an alcohol, etc. and fillers such as cellulose, silica, active carbon, or carbonate are also used. The product is in paste form.
The '142 patent also cites U.S. Pat. No. 5,142,817 as describing sheets or strips formed of a sheet of water-insoluble polymer adhesively bonded to a sheet of a hydrophilic matrix. This matrix may be made of cellulose fibers, polyester, polyacetate, polyvinyl alcohol, or polyoxyethylene glycol. This matrix contains a plasticizer such as polyoxyethylene glycol or a sorbitol solution and also a biologically active product. These strips serve to envelop trees. The biologically active product is released by a humid atmosphere and serves to protect the trees. The biologically active products are stated therein to include pheromones.
Unlike terrestrial insects that live above ground (and can thus orient themselves using chemical cues that disperse at a distance in the atmosphere), termites tunnel underground in soil. Chemicals do not move as freely (if at all) in soil as they do in the atmosphere. Much prior art relates to the release of vapor phase pheromones into atmosphere, but vapor does not travel at any significant distance in soil where subterranean termites tunneling activity occurs. If a true “attractant” is to be developed for practical use, there is a need to deliver “attractive” agents into the soil so that they cause termites, when present, to “make orientated movement toward its sources.” For example, U.S. Pat. No. 6,216,960 relates to a sustained release pheromone dispenser. This device is intended to disperse synthetic sex pheromones into the air to control harmful (flying) insects by disturbing their copulative communication.
Japanese Patent Application No. 62-177040 (publication no. 64-020853) relates to thermoplastic resin powder and cellulose powder impregnated with “a volatile substance.” The compositions of this application are designed to effect the gradual release of the “volatile substance.”
U.S. Pat. No. 5,173,535 (Dow Corning) relates to plastic materials having particles of crosslinked polymers distributed therein, which entrap functional materials for the purpose of a controlled release of the functional material. The functional materials can include fragrances, pharmaceuticals, dyes, biocides (such as contraceptives), pigments, pesticides, pheromones, and insect repellants. This reference does not relate specifically to controlling termites.
There is no prior suggestion in the art that pheromones could be advantageously incorporated in the housing of a bait station to attract subterranean termites foraging in soil. Furthermore, the art does not provide materials that are impregnated with semiochemicals to permit their release into the soil in adequate amounts for extended periods of time while being exposed to a range of environmental conditions.